Background and study aims Ambient air is the most commonly used gas for insufflation in endoscopic procedures worldwide. However, prolonged absorption of air during endoscopic examinations may cause pain and abdominal distension. Carbon dioxide insufflation (CO 2 i) has been increasingly used as an alternative to ambient air insufflation (AAi) in many endoscopic procedures due to its fast diffusion properties and less abdominal distention and pain. For endoscopic retrograde cholangiopancreatography (ERCP), use of CO 2 for insufflation is adequate because this procedure is complex and prolonged. Some randomized controlled trials (RCTs) have evaluated the efficacy and safety of CO 2 as an insufflation method during ERCP but presented conflicting results. This systematic review and meta-analysis with only RCTs evaluated the efficacy and safety of CO 2 i versus AAi during ERCP. Methods A literature search was performed using online databases with no restriction regarding idiom or year of publication. Data were extracted by two authors according to a predefined data extraction form. Outcomes evaluated were abdominal pain and distension, complications, procedure duration, and CO 2 levels. Results Eight studies (919 patients) were included. Significant results favoring CO 2 i were less abdominal distension after 1 h (MD: -1.41 [-1.81; -1.0], 95 % CI, I² = 15 %, P < 0.00001) and less abdominal pain after 1 h (MD: -23.80 [-27.50; -20.10], 95 %CI, I² = 9 %, P < 0.00001) and after 6 h (MD: -7.00 [-8.66; -5.33]; 95 % CI, I² = 0 %, P < 0.00001). Conclusion Use of CO 2 i instead of AAi during ERCP is safe and associated with less abdominal distension and pain after the procedure.